From: Gao Xiang <gaoxiang25@huawei.com>
Date: Tue, 7 Jan 2020 02:25:46 +0000 (+0800)
Subject: erofs: fix out-of-bound read for shifted uncompressed block
X-Git-Tag: Ubuntu-5.3.0-43.36~66
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=8024da557333ebf899957ed08cb5281bab8d1346;p=mirror_ubuntu-eoan-kernel.git

erofs: fix out-of-bound read for shifted uncompressed block

BugLink: https://bugs.launchpad.net/bugs/1867051

commit 4d2024370d877f9ac8b98694bcff666da6a5d333 upstream.

rq->out[1] should be valid before accessing. Otherwise,
in very rare cases, out-of-bound dirty onstack rq->out[1]
can equal to *in and lead to unintended memmove behavior.

Link: https://lore.kernel.org/r/20200107022546.19432-1-gaoxiang25@huawei.com
Fixes: 7fc45dbc938a ("staging: erofs: introduce generic decompression backend")
Cc: <stable@vger.kernel.org> # 5.3+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
---

diff --git a/drivers/staging/erofs/decompressor.c b/drivers/staging/erofs/decompressor.c
index 1fb0abb98dff..0dbd7799c627 100644
--- a/drivers/staging/erofs/decompressor.c
+++ b/drivers/staging/erofs/decompressor.c
@@ -303,24 +303,22 @@ static int shifted_decompress(const struct z_erofs_decompress_req *rq,
 	}
 
 	src = kmap_atomic(*rq->in);
-	if (!rq->out[0]) {
-		dst = NULL;
-	} else {
+	if (rq->out[0]) {
 		dst = kmap_atomic(rq->out[0]);
 		memcpy(dst + rq->pageofs_out, src, righthalf);
+		kunmap_atomic(dst);
 	}
 
-	if (rq->out[1] == *rq->in) {
-		memmove(src, src + righthalf, rq->pageofs_out);
-	} else if (nrpages_out == 2) {
-		if (dst)
-			kunmap_atomic(dst);
+	if (nrpages_out == 2) {
 		DBG_BUGON(!rq->out[1]);
-		dst = kmap_atomic(rq->out[1]);
-		memcpy(dst, src + righthalf, rq->pageofs_out);
+		if (rq->out[1] == *rq->in) {
+			memmove(src, src + righthalf, rq->pageofs_out);
+		} else {
+			dst = kmap_atomic(rq->out[1]);
+			memcpy(dst, src + righthalf, rq->pageofs_out);
+			kunmap_atomic(dst);
+		}
 	}
-	if (dst)
-		kunmap_atomic(dst);
 	kunmap_atomic(src);
 	return 0;
 }